Various methods and aqueous cleaning solutions have been used for the removal of small residual particles and contaminants from surfaces, such as a wafer surface in the fabrication of semiconductor-based structures and devices. A post-process clean is typically conducted to remove residual particles remaining on the surface after a processing step such as etching, planarization, polishing, sawing, film deposition, etc., prior to performing another device fabrication step such as a metallization, gate or device formation, etc. If residues or contaminants remaining from a process step are not effectively removed, various fabrication problems and defects in the finished integrated circuit device can arise. For example, conductive residual particles (i.e., metals) that remain on a surface feature can cause such problems as shorts between capacitor electrodes or other electrical failures, and non-conductive contaminants on a feature such as particles (e.g., SiO2, polysilicon, nitride, polymers, etc.) from a chemical mechanical planarization or polishing (CMP) or other process can cause problems such as the failure in adhesion of subsequent layers, a loss of critical dimension of the formed feature, or pattern deformation in that area leading to yield loss. Current technology nodes (e.g., 65 nm and smaller) require a high level of surface cleaning, including the removal of remnant particles while maintaining other surface materials intact. At each technology node, the presence of ¼-pitch remnant particles is considered to be a yield inhibitor.
A widely used cleaning technique to remove surface materials is an RCA clean which conventionally includes first applying an aqueous alkaline cleaning solution known as a Standard Clean 1 (SC1) to remove particle contaminants, which consists of a dilution of ammonium hydroxide/hydrogen peroxide (NH4OH/H2O2) followed by a deionized (DI) water rinse. To remove metal contaminants, an aqueous acidic cleaning solution known as a Standard Clean 2 (SC2) composed of a hydrochloric acid/hydrogen peroxide (HCl/H2O2) dilution is often applied, followed by a second DI water rinse. Other wet cleaning methods used for cleaning residues from structures include, for example, a piranha clean using a sulfuric acid based mixture (e.g., H2SO4/H2O2), a buffered oxide etch solution, and fluorine-based aqueous chemistries.
The small particles or contaminants resulting from fabrication steps are held to a surface such as by electrostatic forces and become entrenched, typically require relatively large forces to remove them. Cleaning solutions are often applied in conjunction with acoustic energy (i.e., ultrasonic or megasonic energy), high pressure spraying techniques, mechanical scrubbing techniques with a pad or brush, etc. to enhance the cleaning action of the solution to remove materials and dislodge particles from the wafer surface. However, acoustic cleaning and spraying techniques apply forces in all directions, which can damage sensitive structures or alter critical dimensions without effectively removing all of the particulate contaminants from the substrate. In addition, many cleaning solutions can attack and/or dissolve the structures formed in the fabrication step.
It is difficult to get acceptable particle removal from a substrate surface without adversely affecting fabricated structures or other surface materials using conventional technologies.